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Day 55 - Polaron IV and booster flights

The boosters and main stage are placed empty
onto the launcher, and then the launch rail is
locked in place.

We then fill the boosters with water, and
last of all fill the main stage with foam/water
mix before fitting the nosecone.

Polaron IV is directed slightly into the
wind to allow the rocket to drift back.

We had another excellent
launch day with the
NSW Rocketry Association (NSWRA) this weekend.
When I woke
at 5:30am I heard a really strong
wind was blowing. The wind speed certainly put us out of our
launch criteria. However, we finished
packing and headed out to the site hoping
the breeze would die down by the time
launches started.

Launch Day Events

When we arrived the breeze was still
blowing pretty hard, so we set up the new
launcher and waited. The pyro rocket
guys had to angle their launch rods
quite a way into the wind as well. We
watched a few launches as the breeze
started easing off a little. We finally
decided to launch around 9am. Photos of
the pyro rockets will be available
here.

First launch of the boosted Polaron IV
rocket went well. We launched the rocket
at only a conservative pressure of 110psi
(7.6 bar). The rocket took off
vertically and the boosters all
separated simultaneously. The main stage
continued to power vertically, although
it looked like a gust of wind caught the
rocket and pitched it over. This caused
it to gain less altitude than expected
on review of the altimeter data. The
maximum altitude reached was 104 m
(341'). This was a little disappointing
but we knew that the rocket did not fly
the optimum flight path.

We were really happy with how the
onboard video turned out. We didn't see
any of the compression artifacts or
stuttering as we did last time. Because
it was a bright sunny day the video
quality was excellent.

The video showed us that the parachute
deployed right around apogee, but the
altimeter data again showed that it took
the parachute about 1 second to fully
open. I set the flight computer deploy
delay to a full second longer than what
the simulator predicted because with the
use of foam you get that more protracted
thrust phase. It turned out to be about
the right timing.

The rocket landed softly in the
grass, but was only a couple of meters
from hanging up in a tree.

By the second launch, the wind died
down more and the flight was a lot
better. All the rocket parameters were
the same as the first launch. The
boosters again separated simultaneously
and the rocket went up vertically again.
It fish-tailed a little which was
probably caused by the wind still, but
did not pitch over as much as last time.
This time it went to 144m (473').
We believe the rocket will go over 500'
on a less windy day with the same setup
and pressures.

The parachute again opened right at
apogee. You can hear the deploy servo
activate, and see the parachute come out
in the on-board video. Again the
on-board footage turned out excellent.
The video still had the lagging sound
problem, but we fixed it in our video
editor.

The rocket landed on soft grass well
downrange.

Our last rocket for the day was the
newly repaired Hyperon. It flew
relatively well and was
buffeted by the wind as well. The parachute
opened at apogee and came down nice and
gentle.

We were really happy to walk away on
the day without the need to do any
repairs.

I am
including the video on both YouTube and
MySpace as sometimes one or the other are
unavailable.

(If the video does not play, try the latest
Flash player from Macromedia)

Video and Image Analysis

We reviewed a lot of the video from
various angles and frame by frame to try to
understand how the main stage and boosters
behave in flight.

All three boosters entered their air
pulse phase within ~80milliseconds of
each other. This did not appear to cause
the rocket to pitch in any one
direction. It does look like the
boosters may have been slightly
misaligned and caused the rocket to
roll. It was even more evident as the
last booster dropped off.

One of the boosters could be seen
striking the fin as it separated, but no
damage was done, and did not affect the
trajectory.

The fish-tailing was likely to have
been caused by the gusty conditions, and
this would have washed quite a bit speed
off the rocket. (Hence the large
discrepancy between flight 1 and 2 in
terms of altitude)

The following is a pyro rocket
highlights video from the day shot from our
camera.

What's Next?

These flights were really only prototype
flights to see how well the concept works.
There are many things that can be optimised
and will be carried out over the next weeks
and months. One of the biggest issues is the
weight. Polaron IV on these flights weighed
in at a hefty 928grams empty! We are going
to attempt to shave at least 200 grams from
this.

We will increase the pressures to at
least 120psi for the main stage and
130-140psi for the boosters. The launcher
allows us to supply different pressures to
the main stage and boosters.

In the longer term, the boosters will increase in both capacity and length. The
main stage will also be increased in length
and volume. We want to try the narrower Hyperon rocket with this arrangement as
well.

Next Update

In the next update we will
present the full details of the launcher,
the Polaron IV rocket and booster separation
arrangement. The update will also include a
video of the first launcher tests using the
dummy main stage.

Fast takeoff, some
spin, but quite stable. The boosters
released simultaneously, rocket
pitched over due to wind gusts.
Parachute opened a little past
apogee. Good landing. Good video and
good altimeter data.

Fast takeoff, some
spin, but quite stable. The boosters
released simultaneously, rocket
fish-tailed somewhat but mostly
vertical. Affected by wind gusts.
Parachute opened right at apogee.
Good landing. Good video and good
altimeter data.